Apparatus and methods for locating an object are known in the art. A missing vehicle locator system is described in U.S. Pat. No. 5,418,736 issued to Bird. The vehicle locator system uses one or more GPS systems in conjunction with a GPS antenna, a receiver/transmitter, a telephone with associated antennas, and a modem mounted in a vehicle whose position is to be monitored. A paging request is issued and received by a paging responder in the vehicle. The paging request causes the modem to interrogate the GPS receiver to determine the current position of the vehicle. The current position of the vehicle is transmitted via a cellular telephone link to notify a vehicle location service center of the current location of the vehicle.
Other known location determination techniques include the use of a Loran or a Glonass satellite based system. Another object location system is described in U.S. Pat. No. 5,576,716 to Sadler for locating lost or stolen property. This location system includes a GPS module, a microcomputer, a modem, and a telephone, all of which must be installed in the vehicle. The system described regularly and automatically computes the position of the property for transmission via the phone link to a central receiver/transmission station.
In the context of object locators, low-power transmissions are subject to signal corruption due to noise, static, and signal interference. Extracting information from a signal in the presence of such interference and noise is very difficult when the information signal is of the same order of magnitude as the noise sources. My issued U.S. Pat. No. 7,791,470, the entire content of which is incorporated herein by reference, addresses issues with noise by taking advantage of acquired frequency knowledge. This allows for synthesis of a time and phase coherent response to accurately determine location with a low-power transponder. A hand-held remote locator (RL) device is used to locate a transponder or micro-transponder (MT). The user activates the RL to transmit a multi-frame ping to the MT in a slow ping mode, where the MT transmits reply messages when the multi-frame ping is received The RL calculates a distance between the RL and the MT using the time-of-flight (TOF) between the transmission of a ping and the receipt of a reply. The user can then engage a fast ping mode, where the RL transmits the multi-frame ping at an increased rate. The user then extends the RL device away from their body and turns through at least a partial arc length about their center line such that data is collected including compass readings, Doppler information, and distance calculations. The directional location for the MT is determined by the RL using the collected data.